This invention relates generally to moldable compositions, and more specifically, to water-based, polymeric resin doughs which are neither crosslinked nor gelled.
Traditional moldable compositions and modeling doughs incorporated starch as a filler material. Such doughs, however, had a tendency to flake, crack, and crumble in both the wet and dry stages. These traditional doughs would also typically shrink upon drying. Furthermore, these doughs often demonstrated discoloration upon drying and left a residue on the user""s hands. Moreover, traditional modeling doughs were characterized by poor plasticity, poor dry strength, and substantial drying shrinkage.
Plasticity is the property of a wet dough or clay that permits deformation by application of a relatively slight pressure and retention of the deformed shape after release of the pressure. This property distinguishes the dough in its wet stage from its dry stage. Traditional starch-based modeling doughs have a tendency to crack when dry and are not easily shaped in the dry state by sanding or filing. Furthermore, the user cannot easily add wet dough to the existing dried sculpture. In addition, traditional starch-based modeling doughs are not carveable after they have dried.
Still another drawback with many conventional water-based doughs is that they are often heavy and difficult to manipulate or mold. Dense, heavy doughs are particularly difficult for children to manipulate. Even in the case of an adult artist, dense, heavy doughs limit the shapes that can be created without the dough falling apart.
As mentioned above, another problem with typical water-based doughs is that they experience a loss of volume (shrinkage) upon drying. Because water accounts for a large portion of the volume of the dough in its wet stage, water loss upon drying results in a loss of volume in the resulting molded product.
Discoloration upon drying is another problem seen with typical water-based doughs and is compounded by the dry shrinkage discussed above. As the volume decreases, the relative concentration of pigment increases and the color darkens. In some cases, other components (e.g. a salt) preferentially precipitate and form a crusty, hazy surface on the dried artifact.
Other drawbacks of conventional water-based doughs include the fact that many of them would leave a residue on the user""s hands, and that they can stain or damage textiles, carpets, furniture, etc., with which they come into contact.
Some of the above drawbacks of conventional modeling doughs were addressed through later work on dough formulations which led to the development of water-based modeling doughs comprised of a gelled (crosslinked) polymeric resin, water, and a filler material other than starch. More particularly, these later doughs often used poly(vinyl alcohol) (PVA) as the resin, and added a gellant to cause the crosslinking of the poly(vinyl alcohol). The addition of the gellant, and the subsequent crosslinking of the resin, resulted in a cohesive, water-soluble resin system. When the water evaporated, the dried, gelled, polymer resin material system was durable and lightweight. U.S. Patents which relate to gelling the PVA are: U.S. Pat. No. 5,171,766 to Mariano et al., U.S. Pat. No. 5,364,892 to Miller et al., U.S. Pat. No. 5,498,645 to Mariano et al., and U.S. Pat. No. 5,506,280 to Miller et al.
The above four patents all disclose the use of a gelling agent in conjunction with poly(vinyl alcohol) to form a modeling dough. These references teach that the use of a gelling agent, such as a water soluble borate salt, causes the resin to gel (or crosslink). The result, according to these patents, is a modeling dough which demonstrates wet ductility and low stickiness.
The known doughs incorporating crosslinked poly(vinyl alcohol) were generally pliable, lightweight, left little or no residue, and demonstrated little shrinkage and discoloration upon drying. These later doughs were not without problems, however.
The doughs incorporating crosslinked poly(vinyl alcohol) often demonstrated poor stability, short use time, and stiffer textures. For example, if a fully hydrolyzed poly(vinyl alcohol) co-polymer is used, the product tends to flake because the crosslink density is not high enough. On the other hand, if a partially hydrolyzed poly(vinyl alcohol) co-polymer is used, storage stability and usage time become a problem. The storage problem is due in large part to the fact that as time passes the pH of the system decreases. With lowered pH comes a concomitant reduction in crosslink strength which results in a sticky dough, and a sticky dough does not store well.
A related problem with partially hydrolyzed poly(vinyl alcohol) crosslinked doughs is insufficient usage time. Typically, a user has only about an hour or so to perform the molding he or she desires. This is because once the package is open, exposing the dough to air, rapid further crosslinking occurs and the dough becomes stiff.
Thus, with either fully hydrolyzed poly(vinyl alcohol) doughs, or partially hydrolyzed poly(vinyl alcohol) doughs, problems are encountered. The drawbacks discussed above suggest the need for a water-based modeling dough that has, among others, the properties of pliability, wet ductility, extrudability, joinability, color stability, long usage time, and good storage stability. The compound suggested also ought to accept components intended to meet various needs or expectations of its users, such as colorants or other visual modifiers, tactile modifiers, or odorants.
The present invention provides a moldable composition, such as a modeling dough, comprising a polar polymeric resin, a filler, a thickening agent, a humectant, and a solvent. The moldable composition of the present invention provides a pliable dough having good storage stability, wet ductility, extrudability, joinability, color stability, and bouncing ability. Another favorable characteristic of the dough according to the present invention is that it demonstrates good useage time, and does not rapidly dry upon exposure to air. The present invention also provides a method of making a moldable composition which exhibits the above described qualities.
A preferred embodiment of the present invention comprises poly(vinyl alcohol) in an amount ranging from 0.5-15% by weight, a filler in an amount up to 50% by weight, boric acid in an amount ranging from 0.1-3% by weight, a humectant in an amount up to 30% by weight, and water in an amount ranging from 20-70% by weight.